Photochemical recording process

ABSTRACT

PROCESS OF REPRODUCTION USING A RECORDING LAYER CONTAINING HEXACYANOFERRATE (III) IONS AND A SUBSTANCE PROVIDING IONS OF SELECTED METALS, PREFERABLY AN N-TYPE PHOTOCONDUCTOR. THE LAYER IS EXPOSED TO AN ELECTROMAGNETIC RADIATION IMAGE REDUCING THE HEXACYANOFERRATE (III) IONS IN THE EXPOSED REGIONS TO HEXACYANOFERRATE (II) IONS. THE EXPOSED LAYER IS DEVELOPED BY CONTACTING UNIFORMLY WITH AN AQUEOUS DEVELOPING SOLUTION CONTAINING A DYE INTERMEDIATE WHICH IS OXIDIZABLE INTO A DYE. THE HEXACYANOFERRATE (III) IONS IN THE UNEXPOSED REGIONS OXIDIZE THE DYE INTERMEDIATE AND ARE IN TURN REDUCED TO HEXACYANOFERRATE (II) IONS WHICH COMBINE WITH THE METAL IONS TO FORM A PRECIPITATE HAVING A STRONG AFFINITY FOR THE DYE OXIDATION PRODUCT. IF THE EXPOSURE IS THROUGH A POSITIVE ORIGINAL, A POSITIVE COPY IS OBTAINED SINCE THE IMAGE AREAS OF THE ORIGINAL SHIELD THE CORRESPONDING AREAS OF THE RECORDING LAYER FROM EXPOSURE. A LAYER CONTAINING PHOTOCONDUCTIVE ZINC OXIDE IS ESPECIALLY PREFERRED.

United States Patent US. Cl. 96-49 Claims ABSTRACT OF THE DISCLOSURE Process of reproduction using a recording layer containing hexacyanoferrate (III) ions and a substance providing ions of selected metals, preferably an n-type photoconductor. The layer is exposed to an electromagnetic radiation image reducing the hexacyanoferrate (III) ions in the exposed regions to hexacyanoferrate (II) ions. The exposed layer is developed by contacting uniformly with an aqueous developing solution containing a dye intermediate which is oxidizable into a dye. The hexacyanoferrate (HI) ions in the unexposed regions oxidize the dye intermediate and are in turn reduced to hexacyanoferrate (II) ions which combine with the metal ions to form a precipitate having a strong affinity for the dye oxidation product. If the exposure is through a positive original, a positive copy is obtained since the image areas of the original shield the corresponding areas of the recording layer from exposure. A layer containing photoconductive zinc oxide is especially preferred.

This invention relates to recording and reproducing of information, which is provided in the form of electromagnetic radiation.

The iron ferricyanide system based on the photochemical reduction of hexacyanoferrate (lII) ions is well known.

According to the type of iron ions used in the development, a negative or positive blue-print is obtained. So, the development of a recording element containing an image differentiation in the form of non-exposed areas containing hexacyanoferrate(III) ions and exposed areas containing practically exclusively hexacyanoferrate(II) ions by means of iron(IlI) salts gives an intense blue precipitate with hexacyanoferrate(II) ions on the exposed areas (Prussian blue), whereas by means of iron(II) salts an insoluble blue precipitate of iron(II) hexacyanoferrate(IlI). (Turnbulls blue) is obtained in the nonexposed areas together with a bluish-white precipitate of iron(II) hexacyanoferrate(II) in the exposed areas. According to the blue-print technique the positive reproductions have always a bluish background.

There has now been found a method for an improved production of positive prints within a broad spectrum of colours by means of hexacyanoferrate(HI) ions as lightsensitive'substance, which method comprises the steps of exposing to active electromagnetic radiation a light-sensitive element (supported or self-supporting layer) containing hexacyanoferrate(III) ions and ions of the metals selected from the group of zinc, cadmium, mercury, copper, silver, gold and lead, preferably those ions that in Water form a precipitate with hexacyanoferrate(II) ions, and treating the exposed element with a compound that can react with the hexacyanoferrate(III) ions left in the unexposed areas, whereby a visible image is obtained.

By active electromagnetic radiation is understood electromagnetic radiation having such a wavelength and energy that it' effects in recording materials according to the present invention a photochemical reduction of hexacyanoferrate(III) ions to hexacyanoferrate(II) ions.

'According to a particular embodiment the sensitivity of the recording element is improved by an n-type inorganic photoconductive substance used in intimate contact with the hexacyanoferrate(III) ions during the exposure.

Photoconductive substances that are preferably used are inorganic zinc compounds known for their photoconductive properties, e.g. zinc oxide. When use is made of such a photoconductive compound zinc ions can be provided by the photoconductor itself, so that no other compounds providing ions of zinc, cadmium, mercury, copper, silver, gold or lead need to be present. An n-type photoconductor that does not provide such ions is, e.g., titanium(IV) oxide.

The recording layer preferably contains from 0.05 to 40% by weight of a compound providing hexacyanoferrate(III) ions, but a larger amount may be present.

The content in the recording layer of the compound or compounds providing the cited metal ions may vary within wide limits since the n-type photoconductor itself may provide said ions. Thus, the recording layer may contain from 90 to 5% by weight of such compounds. Preferred compounds other than the photoconductive compounds are, e.g., zinc lactate, lead acetate, cadmium sulphate, copper(II) sulphate, mercury(II) nitrate, silver lactate, and gold(III) chloride. As can be learned from the examples with sparingly water-soluble zinc or mercury(1I) compounds good results are obtained.

By the exposure to active electromagnetic rays the hexacyanoferrate(III) ions are reduced to hexacyanoferrate(II) ions, which have no oxidizing power. The hexacyanoferrate(lll) ions left in the unexposed areas are contacted, e.g., with an oxidizable colour-changing or colour-forming substance or composition such as a leucobase of a dye, an aromatic or heterocyclic amine, or a mixture of oxidatively dye-forming compounds such as p-phenylene diamine compounds, organic hydrazine developers, such as fi-arylsulphonylhydrazines, amidrazones, heterocyclic hydrazones and their vinylene homologues which can oxidatively couple with amines, phenols and reactive methylene compounds as described, e.g., in the United Kingdom patent specification 990,628 and Ang. Chem. (1958) No. 9, p. 215-222.

The solution used for treating the exposed recording element containing a substance or composition that changes its colour or forms a dye by an oxidative treatment is called hereinafter the developing liquid.

According to a preferred embodiment the development is carried out with a liquid containing a leuco base of a dye. Such a leuco base is preferably used in a concentration of 0.5 to 2% by weight in an aqueous solution having a pH of 7 to 1. By the acid contained in the developing liquid ions of the type mentioned above can be set free from metals or metal compounds (e.g. metal oxides, bicarbonates or carbonates), which are incorporated in pigment form in the recording element. So, e.g., zinc ions can be set free from zinc oxide.

' During the development said metal ions of zinc, cadmium, mercury, copper, silver, gold and lead form a precipitate with the hexacyanoferrate(II) ions, which are formed from the hexacyanoferrate(III) ions by the oxidation of the leuco base of the other oxidizable colourforming substance and accelerate the oxidation of the latter. The hexacyanoferrate(II) percipitate, e.g., with zinc ions is white and has a strong adsorption power for cationic compounds, such as cationic dyes e.g., the dyes formed by the oxidation of leucoarylmethane dye compounds are of cationic nature and consequently due to the mordanting effect of the hexacyanoferrate (II) precipitate will strongly adhere thereto, so that according to the invention erasure-proof prints of the most colours can be obtained.

Leuco compounds that are suited for the production of cationic dyes are described in the United Kingdom patent specification 1,032,264.

. According to another preferred embodiment, aromatic and heterocyclic amines are used for oxidatively forming a dye e.g., the amines described in the published Dutch patent application 292,922. In acidic medium these amines are readily oxidized by hexacyanoferrate(III) ions to dyes under the catalytic influence of the above-mentioned metal ions as is also the case with the leuco bases mentioned above. If the developing liquid contains said amines it is. preferably an aqueous liquid having a pH of 7 to 1 and incorporating these amines in a concentration of 0.5 to 2% by weight.

The recording element according to the present invention when not containing a photoconductor in pigment form has not to contain a binder, and may be prepared by simly soaking a porous paper with a solution containing hexacyanoferrate(III) ions (e.g., provided by an alkali metal hexacyanoferrate(III)) as Well as the said metal ions occasionally together with a dye-forming component that oxidatively reacts with another component present in the developing solution.

The developing liquid may contain a softening or swelling agent for the binder wherein the photoconductive substances have been dispersed. In this way the penetrating power of the oxidizable substance is improved and consequently the density of the obtained image is increased. Indeed, in this way much more photoconductor grains are reached for increasing the speed of the redox-reaction. As swelling agents for gelatin urea and potassium isocyanate may be used. As swelling agents for hydrophobic binding agents methanol, acetone, dioxan, formamide and dimethylformamide occasionally mixed with water may be applied.

The swelling agent may be applied before or simultaneously with the hexacyanoferrate(III ions to the developing liquid. Further, said liquid may contain, e.g., 0.5 to 20% by weight of a substance that lowers the surface tension. In this respect are mentioned higher alkyl sulphates, higher alkyl quaternary ammonium salts, water-soluble fatty acid salts, and water-soluable polyoxyethylene compounds.

A recording layer according to the present invention containing a n-type photoconductive pigment contains a binder wherein the photo-conductive substance, e.g., photoconductive zinc oxide, is dispersed.

If a hydrophobic water-impermeable binder is used, care has to be taken that the photoconductive grains protrude from the recording layer surface. Preferably the photoconductive grains are dispersed in a hydrophilic water-permeable binder. Examples of usable binders are urea-formaldehyde resins, dimethylolmelaminc-formaldehyde resins, copoly(vinyl acetate/ vinyl laurate) (80/20) and hydrophilic colloids such as gelatin.

The concentration of the n-type photoconductive substance is preferably in the range of 50 to 90% by weight in respect of the total weight of the recording layer.

As n-type photoconductive substances white photoconductive zinc oxide and titanium(IV) oxide are preferred, which substances can be spectrally sensitized as is known from common electrophotography or can be doped, e.g., with aluminium and/or chromium ions. Preferably use is made of photoconductive zinc oxide prepared according to the French process, viz zinc oxide containing traces of zinc. The spectral sensitivity of the n-type inorganic photoconductive substances can be increased, e.g., by spectrally sensitizing dyes known for that purpose, e.g. those described in United Kingdom Patent Specifications 1,020,504 and 1,020,506, and in US. Pat. 3,507,692 and U8. patent application Ser. Nos. 639,905 and 665,219.

In general the photoconductive substances are inherently sensitive to light of a wavelength range of 3650 to 4000 angstroms. The exposure energy necessary to activate the photoconductor varies with the type of photoconductor, its sensitization, the amount of binder and other ingredients present in the recording layer. All kinds of exposure devices may be used but high energy light sources, e.g., high pressure mercury vapour bulbs, are preferably used.

During its storage the recording element need not to contain the hexacyanoferrate(III) ions; these may be applied immediately before the exposure to the recording element containing (a) metal ion(s) of the cited type. The storage stability of the solution containing the hexacyanoferrate(III) ions can be increased by the incorporation of traces (10* molar parts in respect of the hexacyanoferrate(III) ions) of a stronger oxidans, e.g., dichromate ions. The hexacyanoferrate(III) ions are preferably applied from an aqueous solution containing said ions in a concentration between 0.5 and 5% by weight.

As supports for non self-supporting recording layers all kinds of supports common of use in photographic materials may be applied.

The photographic material according to the present invention may be handled in dimmed day-light. As lightsources for the exposure preferably a high-energy light source, e.g., high or low mercury vapour pressure tubes, are used.

The recording technique according to the present invention is particularly suited for the reproduction of graphic originals.

The developed image may be used for multicopying, e.g., when a leuco arylmethane dye is oxidatively formed, which dye is soluble in common hectographic spirit du-, plicating liquids. It is to be understood that in that case a laterally reversed print has to be produced on exposure.

The following examples illustrate the present invention.

All the percentages are by weight.

EXAMPLE 1 A subbed polyethylene terephthalate film support was coated at a rate of 1 kg. per 14 sq. m. with a dispersion prepared by ball-milling the following ingredients for 12 hours:

ethanoll000 ccs. zinc lactateg.

Sodiumhexametaphosphate (dispersing agent)-1 g. copoly(vinyl acetate/ vinyl laurate) (80/20)60 g.

The resulting material was wetted with a solution com-' prising:

potassium hexacyanoferrate (III)2 g.

water-5O ccs. methanol-75 ccs.

After having been dried, the material was exposed through a diapositive and developed with a solution comprising:

5 g. of the compound according to the structural formula:

methanol-250 ccs. waterccs. 1.75% aqueous solution of hydrogen chloride-75 ccs.

The developed material was then rinsed in water. A blue positive print was obtained.

EXAMPLE 2 A paper support Weighing 90' g./sq. m. was coated at a rate of 1 kg. per 14 sq. m. with a dispersion prepared by ball-milling the following ingredients for 12 hours:

aqueous solution'of gelatin-'- 8; ethanol-80cm.- r zinclactate-'125 g,

and by adding thereto whilst stirring 250 ccs. of a 10% aqueous solution of gelatin, 5 ccs. of an 11% aqueous solution of saponin, and 2 ccs. of a 2% aqueous solution of formaldehyde.

After having been dried, the material was wetted with a 2% aqueous solution of potassium hexacyanoferrate(III) and dried again. Subsequently the material was exposed and developed as described in Example 1.

A blue positive image was obtained.

EXAMPLE 4 A paper support weighing 90 g./sq. m. was coated at a rate of 1 kg. per sq. m. with a dispersion prepared by ball-milling the following ingredients for 12 hours:

% solution of copoly(vinyl acetate/vinyl laurate) 80:20) in acetone-200 ccs.

acetone--350 ccs.

sodium hexametaphosphate-l g.

10% aqueous solution of potassium hexacyanoferrate (III)8 ccs.

copper(II) sulphate--10 g.

After having been dried, the material was exposed through a diapositive and developed with a solution comprising;

p,p-tetramethyldiamine-diphenylmethane5 g.

1.75% aqueous solution of hydrogen chloride-75 ccs. methanol-250 ccs.

water-175 ccs.

After having been rinsed with water, the material showed a blue positive image on a light-green background.

EXAMPLE 5 A subbed cellulose triacetate film support was coated at a rate of 1 kg. per 12 sq. m. with a dispersion prepared by ball-milling the following ingredients for 8 hours:

water240 ccs.

ethanol-60 ccs.

photoconductive zinc oxide50 g. dimethylolmelamine-formaldehyde resin-7.5 g. urea-formaldehyde resin5 g.

sodium hexametaphosphate (dispersing agent)0.1 g.

The resulting material was then wetted with a 2% solution of potassium hexacyanoferrate(III) in equal parts of water and methanol, and then dried.

6 Subsequently the material was exposed through a diapositive and developed for a few seconds in a solution comprising:

5 g. of the compound corresponding to the following structural formula:

CH3 k -Q HOSSHttCIi methanol-250 ccs.

water-475 cos. 7 1.75% solution of hydrogen chloride in water75 ccs.

After having been rinsed with water, the material showed a deep blue positive image of the diapositive.

EXAMPLE 6 A's ubbed polyethylene t erephthalaterfilm support was coated at a rate of 1 kg. per 12 sq. m. with a dispersion prepared by ball-milling the following ingredients for 12 hours:

ethanol-J00 ccs.

photoconductive zinc sulphide-5O g.

copoly(vinyl acetate/vinyllaurate) (/20)-1 l g. sodium hexametaphosphate0.2 g.

The resulting material was wetted with a solution comprising:

potassium hexacyanoferrate (III)2 g.

water50 ccs.

methanol-75 ccs.

After having been dried, the material was exposed through a diapositive and developed for a few seconds in a solution comprising:

p,p-tetramethyldiamine-diphenylmethane-5 g. 1.75% aqueous solution of hydrogen chloride-75 ccs. methanol250 ccs.

water--l75 ccs.

After having been rinsed with water, the material showed a blue positive image.

EXAMPLE 7 A paper support weighing g. per sq. In. was coated at a rate of 1 kg. per 12 sq. m. with a dispersion prepared by ball-milling the following ingredients for 12 hours:

20% solution of copoly (vinyl acetate/vinyl laurate) (80/ 20) in acetone250 ccs.

acetone-350 ccs.

sodium hexametaphosphate1 g.

10% aqueous solution of potassium hexacyanoferrate (III)8 ccs.

photoconductive zinc oxide-41 g.

After having been dried, the material was exposed through a diapositive, developed with the developer solution described in Example 2, and rinsed.

A blue positive print was obtained.

EXAMPLE 8 A paper support weighing 90 g./sq. m. was coated at a rate of 1 kg. per 12 sq. m. with a dispersion prepared by ball-milling the following ingredients for 3 hours:

20% solution of copoly(vinyl acetate/vinyl laurate) (80:20) in ethanol150 ccs.

ethanol-400 ccs.

photoconductive titanium(IV oxideg.

sodium hexametaphosphate1 g.

10% aqueous solution of potassium hexacyanoferrate (III)8 ccs.

The resulting material was then further treated as described in Example 3.

A blue positive print was obtained.

We claim: I

1. A photochemical recording and reproduction process comprising the steps of imagewise exposing to active electromagnetic radiation a recording layer containing hexacyanoferrate(III) ions, and a substance which pro vides ions of the metals selected from the group of zinc, cadmium, mercury, copper, silver, gold and-lead, and uniformly contacting the exposed layer with a developing solution containing a compound which oxidizes to form a colored dye incidental to reduction of the hexacyanoferrate(III) ions left in the unexposed areas thereof to hexacyanoferrate(II) ions, whereby a visible image is formed in said unexposedar'eas.

2. A photochemical recording and reproduction process according to claim 1, wherein the recording layer contains a n-typ'e inorganic photoconductive substance.

3. A photochemical recording and reproduction process according to claim 2, wherein the n-type inorganic photoconductive substance is photoconductive zinc oxide.

4. A photochemical recording and reproduction proc ess according to claim 2, wherein the photoconductive substance is titanium(IV) oxide and the recording layer contains zinc ions.

5. A photochemical recording and reproduction process according to claim 3, wherein the photoconductive zinc oxide has been incorporated into a hydrophilic binder.

6. A photochemical recording and reproduction process according to claim 1, wherein the exposed layer is treated with an aqueous solution containing an oxidizable leuco base of a dye.

7. A photochemical recording and reproduction process according to claim 6, wherein the leuco base is a leuco base of a cationic dye. 8. A photochemical recording and reproduction proc-' ess according to claim 6, wherein the leuco base is applied from ,an aqueous medium having a pH of 1 to 7..

9. A process as in claim 1 wherein said recording layer comprises a binding agent containing the metal ion-prow viding substance, said agent being adapted to undergo softening, and said developing solution includes a soften ing agent for said binding agent.

10. A process as in claim. IWherein saidrecording layer and said developing solution are free of iron ions.

References Cited 6/1966 Great Britain 9692 MURRAY KATZ, Primary Examiner M. SOFOCLEOUS, Assistant Examiner US. Cl. X.R. 96-75, 90, 92 

